Hybrid electric vehicles (HEV's) utilize a combination of an internal combustion engine with an electric motor to provide the power and torque needed to propel the vehicle. This arrangement provides improved fuel economy over a vehicle that has only an internal combustion engine. Clutches may be used to control the power flow and during transient vehicle operations, such as pulling up the engine or the electric motor or shifting a transmission, to provide smooth operation for the driver.
During an upshift in a vehicle transmission, a change in inertia occurs in the driveline because the speed ratio across the transmission changes during the upshift. The change in inertia coupled with the changing speed ratio causes an inertia torque in the driveline, or a resultant torque. If the inertia torque is not offset or compensated for, a driveline disturbance or torque hole may occur, where torque delivered to wheels is discontinuous and may be perceived by a user. The shift may not be smooth, and it may be challenging to meet user expectations regarding vehicle drivability and performance.